This invention relates to a method of manufacturing hollow, reinforced plastic composite articles, and, more particularly, to a method of prestressing a filament wound pressure vessel having a thermoplastic matrix.
Composite pressure vessels have typically been fabricated by a filament winding process which utilizes thermoset plastic resins such as epoxies, polyesters and vinylesters. A thermoplastic liner serves as a winding mandrel and the liner is mounted in a filament winding machine. Reinforcing filaments, usually glass, are trained through a liquid thermosetting resin bath and are wound in a helical pattern on the liner. The composite is cured at ambient temperatures or with heat and the liner becomes an integral part of the finished vessel.
Thermosetting resins have long served to meet the performance requirements of a wide range of pressure vessel products. However, these resin systems have well known drawbacks which may include their limited temperature capabilities, unsatisfactory finished product aesthetics, lack of extended durability, lack of appropriateness for recycling and manufacturing related issues such as down time due to clean-up and material handling costs.
Thermoplastic resins are becoming increasingly popular as matrix material in a composite because of better control over the reinforcement/matrix ratio, scrap materials which can be effectively recycled, diminished regulation issues caused by emissions, higher processing speeds for filament winding, and faster changeover, startup and clean up times.
Problems are associated with filament winding commingled thermoplastic and reinforcing materials on a thermoplastic liner to produce a filament wound, thermoplastic pressure vessel. One such problem is associated with the heating operation following the winding procedure. During that operation the wound liner is placed in a fixture and rotated about its longitudinal axis. Heat is applied at a temperature between the melting point range of the wound thermoplastic matrix and the melting point of the liner to fuse the matrix and soften the liner. During the heating operation the liner tends to soften and become distorted.
In some applications that do not require a thermoplastic liner an inflatable rubberized core is coated with a release agent and is filament wound with commingled thermoplastic and reinforcing materials. After the winding and heating operations the core is deflated and removed from the wound pressure vessel.
The inflatable rubberized core is typically made from neoprene or silicone and the heating process may lead to deterioration of the core. The core may become brittle, less resilient, and deformed. When the core is removed from the tank and reused, it exhibits a reduced life cycle and is more prone to failure during use, thus increasing the risk of a faulty finished article.